How Do I Fix The Biggest Mistake Of My Life
by TheAlphaWrites
Summary: Steve has made a mistake by cheating on Tony, and now he must fix what he's broken. Requested. Steve/Tony. AU.


**Disclaimer: All publicly recognizable characters, settings, etc. are the property of their respective owners. The original characters and plot are the property of the author. The author is in no way associated with the owners, creators, or producers of any media franchise. No copyright infringement is intended.**

**Requested by sanemadness, who wanted cheating!Steve for a change :)**

* * *

The door slam resounded around the room and it seemed to give Steve's legs the cue to buckle underneath him. He felt weak and physically sick to his stomach – _but at least now Tony knows_, he tried to reason, _it's better than lying to him_.

_But then he would still be here with you_, another nastier voice reminded him. At this point, he couldn't decide what was worse: the way Tony's face had lit up when he entered the room, still smelling of his slip-up; or the broken, almost resigned, expression that had taken over when he knew, moments before he had swept out of the room.

Steve had to lean against the wall behind him for support and his head fell into his hands. He could feel his finger tips trembling; feel the tears of self-pity and disgust burning the back of his eyes. He didn't wipe them away when they escaped their prison and trailed down his cheeks.

He deserved to feel as much pain as Tony felt. In one split second, with one badly timed decision, he had made the biggest mistake of his life. It was almost ironic that he had been worried that Tony would slip up – he couldn't have been more wrong.

In the suffocating silence, Steve peered helplessly at the sofa, still indented with their forms, and wished he could bring back that moment of happiness, and more importantly, he wondered how he was going to fix this.

* * *

It was days before Tony would speak to him again.

Steve had tried to incite the conversation first, but the man had told him firmly – without even turning to face him – that "I really can't handle talking to you right now Captain Rogers…just…just _go away, please_…" The desperate way he had trailed off, the plead in his voice, had haunted him.

Steve had been in the gym (a place he had found himself returning almost as much as he did before he had met Tony and the rest of the Avengers, when he had felt the loss and confusion of the new world), just taking his frustrations out on his sixth unsuspecting punching bag of the morning, when Tony had approached him. He was sure he appeared like a puppy, eager and needing to please, as he turned his attention to the other man. Stark looked almost dead on his feet, with the blackened skin that surrounded his red, puffy eyes, and the pale almost shallowness of his skin. Steve swallowed uncomfortably, the image forcing a pang in his heart, especially with the knowledge _he_ had caused it. He wanted nothing more than to wrap his arms around the damaged man, like he used to, and try to offer some kind of comfort, some kind of apology, that would take the pain away, but he resisted. He knew it was not wanted. So, instead, he waited arms tense at his side just in case, for Tony to say something – to forgive him, to curse him, to do _anything_.

Tony opened and closed his mouth a few times, before he finally seemed to be able to manage the formation of the words he needed to say. "I…I just want to know who it was…"

Steve sighed uneasily. He didn't really want Tony to know, but he knew he deserved at least that much. To distract himself, he began the process of unwrapping the bandages around his knuckles. "She was, uh, a dame at one of your parties…"

"Her name."

"Daisy, I think…maybe Diane."

He licked his chapped lips, his gaze hardening. "Okay. Daisy or Diane. Now tell me why. Did I…did I do something wrong? I mean, I tried really hard Steve, to know screw this up, I really did. I wanted you to be happy with me…"

"I _am_ happy with you," Steve quickly assured, his expression showing so much certainty and determination that he didn't think Tony could possibly question the truth behind the words, "I just…" he fumbled to find the right words, "It was a mistake Tony, a huge mistake. I don't know what I was thinking – that's it, I _wasn't_ thinking. She meant _nothing_ to me, and I should _never_ have even considered it in the first place. I never meant to hurt you in anyway Tony, you have to believe that."

Tony laughed bitterly. "Yeah well you did, a lot. You have no idea how much of a kick in the teeth it was to hear. I wanted you to want to stay with me, to believe you had made the right decision in picking _me_, over everyone you could have had, and then…I always thought that, if anyone was going to accidently fall into bed with someone else, it would be me. I never thought of how much it would hurt for it to be _you_…"

"What can I do to make this up to you? To convince you I really am sorry?" he questioned, despairingly.

There was a moment of silence before he answered his voice strong and firm, yet so vulnerable, as if he didn't think he'd ever get what he wanted. "I need you to prove that you love me just as much as I love you, and that you want this relationship to work, to succeed – because if you don't, _then what's the point?_"

* * *

The New York air was biting, but Steve couldn't really feel it, even though he was only wearing a pair of sweat pants and a short-sleeved muscle shirt. His bare feet tapped a strange, muffled tune out on the metal flooring of the balcony, as he thought.

"_I need you to prove that you love me just as much as I love you…"_

The words echoed around his head. Tony wanted him to prove his love, but how? It seemed like such a simple request, something that anyone should be able to prove to the one they loved, but for the life of him, he couldn't think of _how_.

Tony wasn't one for grand gestures – names written in the stars, words burnt into the grass outside his bedroom window, like what was usually found in those 80s movies that Natasha had taken great joy in showing him. He couldn't write poetry, could barely string two words of a letter together – and even if he could, what would he say?

No, nothing on a piece of paper, so flimsy and easily broken. Besides he was sure that Tony would want something like that said in person. It was almost cowardly, hiding behind the rehearsed, daintily written words, so you don't have to see how the receiver reacts. If he was going to use words – and he had a feeling he would have to, just to be sure Tony understood completely how he felt – he would have to say them in person.

_Be in the line of fire…_ he thought with a sardonic sourness.

Steve heard her before he saw her. He doubted he could confuse the steady tapping of heels across the flooring for anyone else. He continued to stare firmly out a head of him, too scared to lower his gaze and meet what was sure to be a furious stare. The footsteps stopped on his right, and he waited for her to say something. It didn't take long.

"You know, I'd probably be biting your head off right now, if you didn't look like someone had just killed your puppy," Pepper commented offhandedly.

Steve stubbornly stayed silent, his gaze never wavering. He heard Pepper sigh deeply, before she continued, "Alright Mr. Tall, Blond and Silent, you don't have to answer me. I just thought you should know that I'm not here to yell at you – but god, you should know I want to. No, I want to know why you would even contemplate cheating on Tony. I mean, I honestly thought you were better than that."

"I don't know why…" Steve said through gritted teeth.

"That's a bullshit excuse, and you know it," Pepper shot back bluntly. "There's always a reason why. You can't honestly believe that for a good few minutes at the minimum, your brain went on vacation." She paused for a moment and he felt a hand rest on his shoulder, "I won't tell Tony, if that's what you're afraid of…"

"It's not that…" Steve shook his head. He sighed deeply, thinking back to that night. "W…We'd been fighting, and it wasn't arguing about Tony leaving his underwear on the floor, or about how many times I've watched the Wizard of Oz this week. It was…bad, really bad. And then we had to go to another stupid party, pretend we weren't so angry with each other…Tony was off flirting with every gent and gal that approached him, and I was at the bar. I remember watching him, grumbling angrily to myself, when this dame approached me…"

"Daisy or Diane," Pepper inputted dryly.

He winced. "Uh, yeah, her…she was saying these things, about Tony, about what he was like before his kidnapping, before the start of our relationship a-and…"

"_I guess someone can't change who they are…"_ he remembered the phase distinctively and it made his insides churn. He gritted his teeth against it and continued.

"…I should never have let her get to me. It was careless and stupid a-and I'm never going to forgive myself for betraying Tony like that…"

"He thinks he pushed you to it, you know. That he made a mistake," Pepper whispered.

"He also says that I'm too good for him, and he's wrong about that too," Steve responded. "Tony…he's the one that's too good for me. Yes, I may be Captain America, patriotic, old-fashioned, and Steve Rogers, hopeless lost in the 21st century, but he's Tony Stark: smart, bold, witty, brave, and gorgeous." He licked his lips nervously, "And I know he'll always deny this, but he cares so much, about all of us. He misses Thor when he's gone; battles against Bruce's opinions on himself and the Other Guy. He wants you and Natasha to be happy, and for Clint and Phil to be accepted for that adoption. He wants the world save and to clean the blood from his hands. And he'll do anything in his power to ensure that, even if it means stepping on people's feet. He was even willing to sacrifice his self, on two occasions, to stop Loki – but it's like he doesn't even see that. I'm the one that doesn't deserve him, not the other way around." He stated firmly, before trailing off into a sigh, "And now I'm going to lose him if I don't find a way to prove how much I love him, and I can't think of anyway that will convince him of the truth. You and I both know how stubborn he can be…"

"Steve…" Pepper started, "You're right, we both know Tony so your next move should be easy for you. Just…think back to what he's told you. I'm sure you'll think of something. Oh, and as for what you should say? Just…be honest. If what you say is even half as good as what you've just told me, I don't think he'll have any trouble believing you."

Steve was surprised when she rose herself up to press a kiss to his cheek. She strained a smile and tapped his arm, before turning to leave. "Good luck."

* * *

Tony peered up at him expectantly, his hands stilling over his desktop, and Steve took in a shaky breath. He kept his hands firmly behind his back, holding the object like it was the only think that kept him grounded.

"Steve, I don't have all day…" he retorted.

Steve cleared his throat. "Uh, yes, right, yes of course, I know, just give me…" he licked his lips nervously, "Okay, if been thinking about how I could prove to you how much I love you, and how I could make you believe what I say is true. It's taken me a while to get this right, but um, please just hear me out," he took in a shaky breath, and tried to remember the words he had been trying to prepare for days, "Before the Avengers and before you, I didn't know what to do with myself. I felt alone, lost in his new world that I didn't understand that was apparently 70 years in my future, even though it felt like a split second for me. All I could think about was what I had lost, the people who had died with I was in ice, instead of seeing what I could do now – and you showed me that. You made me realise what the future holds, what my future could hold. You showed me about family, even though we aren't related by blood, and love that's so much than I ever thought it could be. I love you Tony, so much, and I don't deserve you or your love, and I hate myself for harming you like I have. There's no excuse I know, and you have every right to never want to see me again and end our relationship, to shout at me and hurt me just as much as I have hurt you – and I'll be honest, if you do all of that, I would accept it as my punishment. But I hope you won't. I hope you see me as someone worth your time still, and that we can put this all behind us. Because I love you and I want nothing more in this world for this relationship to work. If you left me, I'd might as well be back in the ice because I don't have my life anymore. You mean so much to me Tony, probably more than I can ever put into words, and I will spend the rest of my life trying to fix things between us." He flushed under Tony's blinking stare, "Um, that's it. I've said all I can say, so uh, I'll just leave you to finish working now. Again, I'm sorry to interrupt. Thank you for listening…" he paused in his backing out of the door, "Oh, I forgot this…"

He pulled the object from behind his back and gently lies it on the table in front of him. He shifted awkwardly. "You said you always wanted one when you were little and, uh, you make a good model, so um, yeah…I hope you like it." He finished in a mumble before scrambling out the door.

Tony's hands trailed along the item placed on his desk. A charcoal sketch stared back at him. He could remember that day – he had found out that Steve had never been to Coney Island and had decided to fix that. He remembered asking a passing couple to snap the picture. His fingers absentmindedly traced the curve of Steve's face. He'd captured the moment perfectly. But he hardly could expect anything else.

Steve was good at that kind of thing.

"_You know when I was younger, all I really wanted was a picture with Captain America,"_ he had told Steve once, after some excited kid had rushed up to them, clutching a camera in his hand. He couldn't believe that he had remembered.

Unable to stop, a laugh bubbled in his throat.

* * *

Steve awoke as soon as the guest room door opened around midnight that night. He didn't open his eyes, just stilled, and waited for something to happen. His ears twitched at the padding of bare feet against the flooring, and the squeaking of the springy mattress as someone sat down on it. There seemed to be a moment of hesitation before the body shifted closer to his own, arms through over his waist, legs nudging around his own, a face buried in the back of his neck.

"…Tony?" he breathed into the stillness hopefully.

"Yeah…Yeah, it's me," Tony muttered into his ear, causing the blond to visibly relax into the hold, "Go to back to sleep. We'll talk about this in the morning…"

"Okay," Steve agreed easily. He paused before continuing warily, "I missed you."

"I missed you too."

* * *

**If you have any prompts for Avengers stories, anything you want to see in print, I am open for requests. You can either send me a private message on here, or leave me a message on my tumblr: WhatIMustWrite**


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